Variable mutual conductance amplifier



Jan. 16, 1951 G. H. P. ALMA 2,538,663

VARIABLE MUTUAL CONDUCTANCE AMPLIFIER Filed July 20, 1946 Patented Jan.16, 1951 UNITED STATES;

: ATENT" mos VARIABLE MUTUAL GONDUCTANCE AMELIFIEB Gerrit- HendrikTetrus Alma, EindhoyemNethenlands, assignor to ."HartfordNational Bankand Trust Company, Hartford, Conn, as trustee 9 Claims. (01. 179 -171)In the copending patent application, U. S., Se rial No. 683,710, how..Paten't QNo. 2,5 30,59 11,' i s.-V. sued November. 21,1950, there isdescribedacirwit-arrangement. for the amplification ofi el'ectricaloscillationsby means of at least two, paral. lel- -connected dischargepaths, controlledjby con trolgrids, having characteristic'l curves the,slopes of which vary differently asa functionoi the control-gridvoltage. This circuit ar'r'angemer t'has the characteristicthatuselis'made of discharge paths, of which one has; a comparatively highaverage mutual conductance and a comparatively small grid space and theother'on theecontrary has a comparatively .loW mutual conductance and acomparatively large grid space, provision being made of means whichautomatically ensure that the amplificatiorigin thecase of smallamplitudes of the loscillations to be amplified; is efiected solely, ,orpractically s les. b m ntof, the first-m n ned disch r e path. and'inthe case of large amplitude'sqof; these oscillations, solely orpractically solely bymeans ofithela t-mentioned path."

The automatic change-over from, one, dise hareepatht he. h r can e fe tily. be B1 sures by p yin t the ontrol rids 'a con r l voltage varyingwithjthe amplitude'of' the 'oscillations to be amplified, which voltageblocks the first-mentioned discharge path with comparatively high valuesof the oscillations to be amplified and which infiuencesat the same timethe potential of an auxiliary electrode located in the last-mentioneddischarge path (that-"is the path having the comparatively-small averagemutuallconductarice and the comparatively large grid space),insuchmannerthat this path is blocked in the case of" comparativelylowvalues of the oscillations to be amplified. In'- one form ofconstruction of the circuit-alfrangement described in detaiLthe saidauxiliary electrodeis'connected, via a. resistance, to: theinterconnected anodes of the two" discharge paths, whilst the commonanode circuit of'these paths includes a resistance, preferably high,which is proportioned in'such manner that inthe case of sma llamplitudes. of the oscillations. to be amplified the discharge pathincluding; the auxiliary electrode is blocked.

The invention provides an'. improvement of this circuit-arrangement bywhich the rnagrimumam plification obtainable is raised; The invention isbased on, the recognition of the fact that the saidresistance interposedbetween the auxiliary electrode and the anodes reduces the anode 'imeped cce. nd co q e y .t el nlifi at onone discharge tube I.

2 l According to the invention the auxiliary'electrode' connected to anelectrode placed in the discharge path having'the comparatively'highaverage mutual conductance and. extending through a comparatively smallpart of this'discharge ,path. Apositive voltage is applied to the,auxiliary electrode through a preferably high resistance; the saidelectrode and the said resistance being proportioned in such manner thatin the case of comparatively .smallamplitudes" of the" oscillations tobe amplified the discharge path "comprising the "auxiliary electrode isblocked completely or almost completely;

The auxiliary electrode is preferably con nected direct'to the aforesaidelectrode. order that 'the'inve tion may beflclea'rly understood andreadily carried into effect it"will now be. set out more ful-lyfl with'referenc e to the accompanying drawings 'In, the drawingzf Fig. '1is ,a'schematic diagram of a circuit in accordance with the invention,and

Fig. 2 is a cross-sectional view of the tube included in the circuit ofFig. 1.

The drawing illustrates a circuit-arrangement for the amplification oflow-frequency oscilla tions, in which use is "made of two. "dischargepaths (A and B); .both'of whichfare housed in control gri'djZja screengrid consisting of two parts 3 and 3",v a suppressor grid 4, an'anodeli,and a ca hOde'B Which is connected to suppressor grid'll. The aforesaidauxiliary electrode is iormed by parts 3' of the screen grid.'Ihedischarge path A. which "comprisesth is auxiliary electrode, iscontrolled by a part ofthe control grid which is realized with an unevenwinding pitch. The part of the control grid"located-in theotherdischarge path is WOllIltT'Wlth a constant pitch. .Thetwocontrol-grid'parts are e'lec-- tricallythrough-connected. Thesuppressor grid 4,"the anode 5 and the cathode 6' serve'atthesametime'for both the discharge paths."

The screen-grid part 3 is connected; via a potentiometer constitutedbytwo resistances '1 and 8, to the positive terminal of a supply of directcurrent voltage (not shown) anjdfviaa condenser 9, to the-cathode 6.

According to the invention'an electrode is located in the discharge pathB," that is the discharge path having the comparatively high averagemutual. conductance and the corn-parad tiyelyjsmall grid space. The saidelectrode,

which is preferablyformed in the shape-Ora rod, extends throughalcomparatively'small partfof This tube comprises 'a,

the discharge path B and is connected direct to the auxiliary electrode3'. The potential of this electrode has little or not influence on thecurrent flowing in the discharge path B. The auxiliary electrode 3 isconnected, through a high resistance ill, to the positive terminal of adirect-current voltage supply (not shown). The electrode l4 and theresistance are proportioned in such manner that in the case ofcomparatively small amplitudes of the oscillations to be amplified thedischarge path A is blocked completely or almost completely. Theauxiliary electrode 3' is connected to the cathode 6 via a condenser H.The anode circuit includes a comparatively high resistance 12. The valueof resistance i0 is, as a rule, higher than that of resistance l2.

The low-frequency oscillations to be amplified are supplied, togetherwith a control-voltage varying with the amplitude of these oscillations,

to the control grid 2. The amplified oscillations can be taken fromresistance i2 through a condenser l3.

The circuit-arrangement operates in a manner similar to that of thepatent application, heretofore mentioned, i. e. a high maximum noiselessamplification (at a low anode current) when the amplitude of theoscillations to be amplified is comparatively small, and anamplification that is very well adjustable when this amplitude iscomparatively large. The high maximum amplification is obtained by meansof the discharge path B which comprises the screen-grid part 3, whereasthe adjustable amplification is brought about by means of the dischargepath A in which the auxiliary electrode 3' is located.

In this case, however, the automatic changeover from one discharge pathto the other is effected in a manner different from that in theaforesaid form of the arrangement described in the patent application,heretofore mentioned.

In the case of a large amplitude of the oscillations to be amplified,hence at a high negative value of the control voltage, the right-handdischarge path is blocked by the control voltage supplied to thecontrol-grid 2, whereas the lefthand discharge path keeps operative. Inthe case of a small amplitude of the oscillations to be amplified, henceat a small negative value of the control voltage, the right-handdischarge path keeps operative, Whereas the left-hand discharge path isblocked completely or almost completely.

This blocking takes place as follows: In the case of a decrease of thenegative value of the control voltage the current of the right-handdischarge path increases. From this current a small portion is derivedby the electrode 14. This portion flows through resistance It to thecathode and consequently brings about at this resistance a voltage drop.The electrode (4 and the resistance lil are proportioned in such mannerthat the voltage drop is so high that the voltage of the auxiliaryelectrode falls below the minimum value required to maintain thedischarge current, so that the left-hand discharge path is blockedcompletel or almost completely. In this case the discharge path Aconsequently contributes to the amplification no longer or substantiallyno longer. I The present circuit-arrangement has the advantage over theform of the arrangement described in the main patent specification,heretofore mentioned, that the anode impedance may have a high value,since the resistance i0 is no longer connected to the anode 5.

A similar result may be obtained by providing the auxiliary electrode 3with an extension which extends through a comparatively small part ofthe discharge path B. In one practical form of construction theauxiliary electrode 3' and the screen grid 3 can, for example, be woundcoaxially, the winding of the auxiliary electrode 3', being continued tosuch an extent that this electrode overlaps a small part of screen grid3.

What I claim is:

1. An amplifying circuit arrangement comprising, first and secondthermionic discharge paths enclosed in an evacuated envelope, said pathsbeing connected in parallel relation and havin cathodes and anodesconnected in common, the first thermionic discharge path having furthera control grid electrode with given spacing between cathode and anodeand given mutual conductance and a screen grid electrode, the secondthermionic discharge path having further a control grid electrode withlarger spacing between cathode and anode and lower mutual conductancethan that of the first thermionic discharge path and an auxiliaryelectrode between the control grid and anode of the second thermionicdischarge path, a source of desired signals, means to couple said sourceto the cathodecontrol grid circuits of the said first and seconddischarge paths, an electrode inserted between the screen grid and anodeof the first thermionic discharge path, and means to couple said latterelectrode to the auxiliary electrode whereby the second discharge pathis blocked upon the source of desired signals reaching in magnitude apredetermined level.

2. An amplifying circuit arrangement comprising, first and secondthermionic discharge paths enclosed in an evacuated envelope, said pathsbeing connected in parallel relation and havin cathodes and anodesconnected in common, the first thermionic discharge path having furthera control grid electrode with given spacing between cathode and anodeand given mutual conductance and a screen grid electrode, the secondthermionic discharge path having further a control grid electrode withlarger spacing between cathode and anode and lower mutual conductancethan that of the first thermionic discharge path and an auxiliaryelectrode between the control grid and anode of the second thermionicdischarge path, a source of desired signals, means to couple said sourceto the cathodecontrol grid circuits of the said first and seconddischarge paths, a resistive element, means to apply a source of directcurrent potential to said auxiliary electrode through said resistiveelement, and an electrode inserted between the screen grid and anode ofthe first thermionic discharge path, said latter electrode connected tothe auxiliary electrode whereby the second discharge path is blockedupon the source of desired signals reaching in magnitude a predeterminedlevel.

3. An amplifying circuit arrangement comprising, first and secondthermionic discharge paths enclosed in an evacuated envelope, said pathsbeing connected in parallel relation and having cathodes and anodesconnected in common, the first thermionic discharge path having furthera control grid electrode with given spacing between cathode and anodeand given mutual conductance and a screen grid electrode, the

- second thermionic discharge path having further .-nals,vmeansto-couple said source controlid c rcuits ,e the is ish s discharge;paths, aresistive e le-me --D y aysource of direct urgent I'non,.'thefirst vthermionicrdi sel se ge path; *further a control ,gridelectrodwith given sp srjiare {the control;

ioni d s h r alate sfiliie O and auxiliary e ec re e h tq he l e and anelectrode having the sh S6 'ted' b'etwe'en the screen" first thermionicdischarge path, said latter electrode connected to the auxiliaryelectrode whereby tne seeenu dischargepathii's blocked Iupon'athe sourceof desired. signals reaching in magnitude a predetermined level. V

4. An amplifying circuit arrangement comprising? first and secondthermionic discharge ipaths enclosed in an evacuated': envelope said:"paths being connectedjn parallel relati ing between cathode and anodeand given mutual conductance and a screen grid electrode, the secondthermionic discharge path having further a control grid electrode withlarger spacing between cathode and anode and lower mutual conductancethan that of the first thermionic discharge path and an auxiliaryelectrode between the control grid and anode of the second thermionicdischarge path, a source of desired signals, means to couple said sourceto the cathodecontrol grid circuits of the said first and seconddischarge paths, a resistive element, means to :apply a source:auxiliary electrode through said resistive element, :and an extensionof the said auxiliary electrode of direct current potential to saidinserted between the screen grid and anode in the :first thermionicdischarge path whereby the second discharge path is blocked upon thesource of desired signals reaching in magnitude a predetermined level.

5. An amplifying circuit arrangement comprising, first and secondthermionic discharge paths enclosed in an evacuated envelope, said pathsbeing connected in parallel relation and havin cathodes and anodesconnected in common, the first thermionic discharge path having furthera control grid electrode with given spacing between cathode and anodeand given mutual conductance, the second thermionic discharge pathhaving further a control grid electrode with larger spacing betweencathode and anode and lower mutual conductance than that of the saidfirst thermionic discharge path and a screen grid electrode comprisingof two parts insulated electrically from each other and insertedrespectively in the first and second thermionic discharge paths, asource of desired signals, means to couple said source to the cathodecontrol grid circuits of the said first and second discharge paths, aresistive element, means to apply a source of direct current potentialto said auxiliary electrode through said resistive element, and anelectrode between the screen grid and anode in the first thermionicdischarge path, said latter electrode connected to the screen gridelectrode in the second discharge path whereby the second discharge pathis blocked upon the source of desired signals reaching in magnitude apredetermined level.

6. An amplifying circuit arrangement comprising, first and secondthermionic discharge 'paths enclosed in an evacuated envelope, said;paths being connected in parallel relation and cans to pf a'rod inridandanode in the and an electnode l l and a o, e of the. fir ,the mionfiiseha l said latter electrode eonnected t' i the' a c e eby-the seco dd hais t oel ed-.-,upon lthe-.source of, desiredsignals reacting inmagnitude apr'edetermined level.

7. An amplifying circuit arrangement comprising, first and secondthermionic dischargepaths enclosed in an evacuated envelope, saidl pathsbeing connected in parallel relation and. having a common cathode andcommon anode, the first thermionic discharge path having: further acontrol grid electrode with given spacing between cathode and anode andgiven mutual conductance and a screen grid electrode, the secondthermionic discharge path having further a control grid electrode withlarger spacing between cathode and anode and lower mutual conductancethan that of the first thermionic discharge path and an auxiliaryelectrode between the control grid and anode of the second thermionicdischarge path, a source of desired signals, means to couple said sourceto the cathodecontrol grid circuits of the said first and seconddischarge paths, a resistive element, means to apply a source of directcurrent potential to said auxiliary electrode through said resistiveelement,

and an electrode having the shape of a rod inserted between the screengrid and anode of the :first thermionic discharge path, said latterelectrode connected to the auxiliary electrode Whereby the seconddischarge path is blocked upon the source of desired signals reachin inmagnitude a predetermined level.

8. An amplifying circuit arrangement comprising, first and secondthermionic discharge paths enclosed in an evacuated envelope, said pathsbeing connected in parallel relation and having a common cathode andcommon anode, the first thermionic discharge path having further acontrol grid electrode with given spacing between cathode and anode andgiven mu-- tual conductance and a screen grid electrode, the secondthermionic discharge path having further a control grid electrode withlarger spacing between cathode and anode and lower mutual conductancethan that of the first thermionic discharge path and an auxiliaryelectrode between the control grid and anode of the second thermionicdischarge path, a source of desired signals, means to couple said sourceto the cathodecontrol grid circuits of the said first and seconddischarge paths, a resistive element, means to apply a source of directcurrent potential to said auxiliary electrode through said resistiveelement, and an extension of the said auxiliary electrode insertedbetween the screen grid and anode of the first thermionic dischargepath, said latter electrode connected to the auxiliary electrode wherebythe second discharge path is blocked upon the source of desired signalsreachin in magnitude a predetermined level.

9. An amplifying circuit arrangement comprising, first and secondthermionic discharge paths enclosed in an evacuated envelope, said pathsbeing connected in parallel relation and having a common cathode andcommon anode, the first thermionic discharge path having further acontrol grid electrode with given spacing between cathode and anode andgiven mutual conductance and a screen grid electrode, the secondthermionic discharge path having further a control grid electrode withlarger spacing between cathode and anode and lower mutual conductancethan that of the first thermionic discharge path and an auxiliaryelectrode wound coaxially with the screen grid electrode in the firstdischarge path and between the control grid and anode of the secondthermionic discharge path, a source of desired signals, means to couplesaid source to the cathode-control grid circuits of the said first andsecond discharge paths, a resistive element, means to apply a source ofdirect current potential to said auxiliary electrode through saidresistive element, and an extension of the said coaxially woundauxiliary electrode inserted in the first thermionic discharge pathwhereby the second discharge path is blocked upon the source of desiredsignals reaching in magnitude a predetermined level.

GERRIT HENDRIK PEIRUS ALMA.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,066,284 Ballantine Dec. 29,1936 2,141,303 Jonker Dec. 27, 1938 2,263,825 Laughren Nov. 25, 19412,270,791 Strutt et a1. Jan. 30, 1942 2,315,043 Boucke Mar. 30, 1943

